MK-801 blocked the expression of cocaine-conditioned increases in locomo- tor behavior. MK-801 injections into the n. accumbens on the training day attenuated the development of cocaine-induced conditioning. 6-OHDA lesions of the n. accumbens blocked the expression of cocaine-conditioned effects. A cocaine challenge (2.5-10 mg/k) enhanced the conditioned effects of cocaine when administered during the test day. Stimuli associated with cocaine increase extracellular levels of dopamine in the n. accumbens, but not the striatum or amygdala. D1 and D2 agonists did not produce conditioning even at high doses. Cocaine-conditioned effects are still detectable 30 and 60 days following seven days of conditioning, and six and eight days following three conditioning sessions. Signifi- cant conditioned rotational behavior was found in rats with unilateral 6- OHDA lesions of the nigrostriatal pathways following training with amphetamine. Conditioned increase in locomotor behavior was seen in rats allowed to eat their daily food in activity chambers.